Continuous process for producing sheet metal and clad metal



R. G. SWEET 3,

SHEET METAL AND CLAD METAL July 11, 1967 CONTINUOUS PROCESS FOR PRODUCING Filed April 28, 1964 II I YQQOOOGQOG woo woo 9. 3am F 022.3 :220 woo fiv h m o e o o e o a 0 O o I m I n E Omaha m war.

INVENTOR ROGER G. SWEET 5Y7 MM, WMm TW-KQW ATTORNEYS United States Patent 3,330,654 CONTINUOUS PRQCESS FOR PRQDUCING SHEET METAL AND CLAD METAL Roger G. Sweet, New Canaan, Conn, assignor to Kennecott Copper Corporation, New York, N.Y., a corporation of New York Filed Apr. 28, 1964, Ser. No. 363,086 12 Claims. (Cl. 75-208) This application is a continuation-in-part of my patent application Ser. No. 166,870, filed Jan. 17, 1962, and now abandoned.

This invention relates to the production of metal articles from metal powder, and to an improved process for treating metal powder to form sheets thereof in a continuous and economical manner. More particularly, the invention relates to the production of copper articles from copper powder, and to a continuous process for the manufacture of thin copper strip from copper powder. The invention is also advantageously applicable to the production of sheets, strips, and to the cladding, of one metal on another metal. The metal powder may be in any suitable state of subdivision formed as by grinding or precipitation (hereinafter for convenience called powder) It has been proposed heretofore to compress metal powder into powder sheets, sinter the powder sheets in a reducing atmosphere, and then hot roll the sintered sheets. This technique is not satisfactory, nor is it economically attractive, for the production of sheet metal.

It has also been proposed to mix the metal powder with various organic binders such as volatilizable liquids, form variously shaped articles from the mixture, heat the articles to vaporize the liquid, sinter the articles and work them into various desired shapes. Although many articles and patents have been published on the subject, this kind of technique has had limited acceptance. For example, no commerically satisfactory process has been developed for making strip or sheet metal from coppermetal.

The process of the present invention may be used in producing flat or rolled articles from several metals such as, for example, copper, nickel, tungsten, iron, brass, and zinc, and mixtures of copper and nickel and of copper and zinc. To reduce unnecessary repetition, the invention will be described generally with reference to copper, it being understood that while the invention is particularly addressed to copper and coppermetals (which term is used to refer to copper-containing alloys including a substantial proportion of copper), and to the production of relatively thin strip therefrom, the general aspects of the process are applicable to the other metals and to metal mixtures.

In accordance with this invention the copper powder is mixed with a liquid solution of a plastic material in a volatile solvent to form a mixture that can be extruded or cast in the form of sheets or strips or applied to a belt in a doctoring operation. It is important that the plastic be one that becomes suitably fluid when dissolved in the solvent, tough and preferably flexible when the solvent is removed and decomposable as by depolymerization when heated. u

The process of the invention comprises forming a mixture of the copper powder and solvent-plastic liquid,

3,330,654 Patented July 11, 1967 forming a shaped product for subsequent treatment as a flat sheet or web by applying the mixture to a belt or equivalent surface, heating to evaporate the solvent to form a fairly tough dried sheet of copper powder bound together with the plastic which can be handled and transported to the next stage of operation. The dried sheet is so tough and strong that it can be wound into a roll which can be handled and transported to another operation. In one variation of the process, the dried sheet following solvent evaporation is prerolled to increase the density and cohesion of the particles. The copper and plastic sheet, with or without prerolling, is passed to the sintering operation for the removal of the plastic and the sintering of the copper particles to form a continuous coherent although porous sheet which has utility for certain purposes in this stage. The sintered sheet can be passed directly to cold or hot rolls and rolled into a dense copper sheet which can be used as commercial sheet copper. Strip copper can be formed in a similar manner.

In another adaptation of the process, either the copper powder and solvent-plastic mixture or the tough sheet of copper particles and plastic can be applied over a similar tough copper sheet and the two sheets rolled together. Also, the mixture or the tough sheet can be applied over a wrought sheet of another metal, for examplecleaned steel, and the two engaged sheets passed as a unit through a solvent evaporator, prerolled if desired, through the sintering operation to remove the plastic and then through a rolling operation to form a copper clad steel sheet. Similarly, copper may be clad on a nickel sheet. The process may also be carried out by superimposing two or more dry sheets of similar or unlike metals from which the solvent was removed, prerolling the sheets together, and then sintering and rolling them to form either a thicker sheet or a composite sheet or a clad sheet as the case may be.

The solvent-plastic liquid should be formed of a solvent which is non-reactive with respect to the metal and plastic, be easily vaporized by heating, and inexpensive, and the plastic should form a fluid when dissolved in the solvent, have good binding properties and be heat fugitive, which means that it must be removable on heating leaving carbon or contaminating deposits. The mixture of solventplastic must be capable of holding in suspension a high concentration of powder and be sufliciently viscous that the copper does not settle. As a result of the properties of the powdered metal and the viscous properites 0f the liquid the slurry mixture can be applied as a uniform layer in a doctoring operation on a moving surface or extruded through a casting slot onto a continuously moving surface such as that of a belt. This is an important part of the process because the formation of a uniformly dimensioned continuous sheet or layer of the slurry mixture of solvent-plastic and copper powder is necessary to form a uniform finished sheet or strip of copper. It is advantageous to use a plastic that is soluble in easily volatilized solvents and which decomposes so that there is no residue left on or in the copper powder after sintering. It is highly advantageous from the standpoint of economics and operating procedure to use the smallest possible amounts of solvent and plastic, and in this respect the invention achieves significant advantages. A powder having an average particle size of about 7 microns was found to be very effective.

It is necessary that the plastic be removable from the plastic-metal sheet in a manner not deleterious to the final metal sheet. Paraformaldehyde, polystyrene and polyisobutylene (one such product being sold under the trade name Vistanex) have been found to decompose on heating without leaving residues in the metal. Polystyrene and the product Vistanex polyisobutylene are readily decomposed to volatile products by simply heating as in the sintering furnace at a temperature above about 700 F. in a non-oxidizing atmosphere such as annealing gas (7% H 93% N or hydrogen. No carbonaceous residues or carbon-contaminated products result from decomposing such polymers.

The solvent for the plastic must be removable from the plastic by heating and vaporization and must be non reactive with the copper. Suitable solvents include alcohol, benzene, toluene, xylene, naphtha, white gasoline, parafiin hydrocarbons (hexane, heptane, etc.) and the like. The solvent-plastic liquid is formed by dissolving the plastic in such an amount of solvent that the liquid has the necessary viscosity at normal temperatures to form the desired mixture with the powder. It is necessary that the plastic-solvent metal mixture have viscosity or other physical characteristics such that the metal powder be sufiiciently stable in suspension as to permit the formation of a substantially homogeneous slurry mixture that remains homogeneous over a period of time, and that can be doctored, extruded, or otherwise shaped conveniently into a uniform layer or sheet. The viscosity (or consistency) of a plastic solution is influenced by the molecular weight of the polymer, the solvent, the prior history of the solution including the amount of viscous shear already put into it-as well as the normal variables such as composition, temperature, etc. In general, the higher the molecular weight of the polymer, the smaller the amount one has to use.

An especially effective solvent-plastic composition consists of one part of Vistanex polyisobutylene having an average molecular weight of from 200,000 to 300,000, dissolved in about 20 to 25 parts by weight of naphtha. A solvent-plastic composition of this character can form an elfective product containing about 120 parts by weight of copper powder having an average particle size of about 7 microns.

The copper powder can be produced in any suitable manner as by electrolytic precipitation, air atomization, by grinding or by purchasing it on the market. The particles of copper may vary from, say, 1 to 100 microns (100 microns equal about a 140-mesh screen). In making copper strips a preferred range of particle size appears to be from microns to 44 microns (44 microns equal about a 325-mesh screen).

It has been found that if the metal powder is in too fine a state of subdivision, for example, having an average particle size of less than 1 micron, an inefficient amount of solvent-plastic is required, and it is difiicult to form layers of the metal-plastic mixture thicker than about 0.017 inch. One effective copper powder had an average particle size of 6.9 microns and an apparent density of 2.98 -gm./cc. It was found that a copper powder having an average particle size of 13.5 microns and an apparent density of 3.3 gm./ cc. was especially effective in enabling the use of up to 130 parts of copper, one part of plastic and 18.8 parts of naphtha.

In the application of the process for the continuous production of copper strip, in which the plastic-metal-solvent slurry is extruded, cast or doctored onto a moving belt, the solvent evaporated, the plastic-metal sheet removed and transferred to the sintering belt, the plasticmetal sheet must be removable from the belt. It has been found that some grades of polystryrene and Vistanex polyisobutylene, some grades of metal powder, and some combinations of metal, plastic and solvent, give rise to a i plastic-metal sheet that sticks tenaciously to the underlying metal belt. Vistanex polyisobutylene that has an average molecular weight from about 200,000 to about 300,000 is well suited to form a plastic-metal sheet that can easily be removed from the belt.

One important advantage in the use of a high metal-toplastic ratio is that this further aids in the elimination of sticking to the belt.

One of the surprising characteristics of a dry (solvent evaporated) coherent plastic-metal sheet, which has been prerolled, is that it is sufiiciently tough that it can be pulled, by reason of its strength, through a heating chamber to remove the plastic and to sinter the metal particles.

The accompanying drawing illustrates diagrammatically an arrangement of apparatus for carrying out the process of the present invention, for the continuous production of relatively thin copper sheet or strip.

One way of carrying out an operation in forming a copper sheet in the illustrated apparatus, in accordance with one preferred embodiment of the present invention, can be described as follows. A mixture or slurry of copper powder having a preferred average particle size of from about 6 to about 15 microns was formed by mixing the copper powder with a liquid solvent-plastic containing Vistanex polyisobutylene (average molecular weight 200,000 to 300,000) dissolved in naphtha in any suitable proportion as will appear from the following more detailed examples. The solvent-plastic liquid binder and copper powder were mixed in a stainless steel mixer, and the mixture was stirred while under vacuum for about 30 minutes to remove gas.

The process was practiced by pumping the stirred, degassed mixture to a casting head, from which it was continuously dispersed onto the smooth, highly finished surface of a moving, endless belt, such as a polished, stainless steel belt or a copper-nickel alloy belt. The casting head had an adjustable orifice or slot that was adjusted to spread onto the belt a uniform layer of the slurry. The particular head used was adjustable to permit the layer to vary from 0.010 inch to A3 inch in thickness.

The continuously moving belt and overlying layer of the mixture was then passed through a heating zone, under the infrared heaters, for evaporation of the solvent. The solvent vapors were removed through the gas outlet and may be recovered by well-known means, if desired.

The coherent, dry sheet was then stripped from the surface of the belt, and was passed between the cold rolls to effect a prerolling to increase the density and strength of the sheet. The prerolled plastic-copper sheet was passed continuously onto the metal conveyor belt of the sintering furnace which was synchronized with the speed of the coherent, plastic-copper sheet. In passing through the sintering furnace, the plastic was decomposed and the decomposition products passed out of the furnace through the gas ofltake.

The interior of the sintering furnace was continuously flushed with a stream of a reducing gas, such as a mixture of nitrogen and hydrogen, so as to maintain a non-oxidizing atmosphere. The furnace was heated by electrical resistance units, but hot combustion gases, passed through sealed tubes, can also be used. The final stage of heating, near the discharge end, was at a temperature near the melting point of copper, such as, for example, about 1030" C., to cause the sintering of the particles of copper and to form a continuous coherent copper sheet that is capable of being self-sustaining and that can be transported as such. This sintered, coherent copper sheet is a valuable product in its own right, and has many valuable potential applications. In the demonstration of the invention that is being described, however, this sintered, coherent copper sheet, while still hot and while maintained in the reducing, non-oxidizing atmosphere, was passed between pressure rolls to form a dense continuous sheet.

The sheet was cooled before releasing it to the atmosphere, to prevent oxidation. The sintered sheet may be rolled either hot or cold, depending on the metallurgical properties that are desired.

The invention was also practised in the following way. Two dried, plastic-cohered sheets, of the same or of different metals, prerolled, were brought together and carried through the sintering, to unite them, followed by rolling, to density them. Similarly, a dried, coherent metal-plastic sheet was prerolled onto a wrought sheet of steel, and the two were then sintered and rolled together, to form a clad sheet.

In another way of practising the invention, for forming a copper clad sheet, of copper on steel, a previously cleaned steel sheet of any suitable thickness such as, for example 0.05 inch thick, and of indefinite length, was passed continuously from a supply roll through the operation. The solvent-plastic and copper powder mixture was doetored onto the steel sheet and the operation previously described was carried out. In another variation of forming copper clad steel, the steel sheet was introduced into the sintering furnace and the prerolled copper powder sheet applied directly over the steel sheet and the sintering and rolling operation carried out thereon.

The following examples illustrate the continuous production of copper sheets in greater detail:

Example 1 Copper powder having an average particle size of 6.9 microns, as determined by an air permeability method, an apparent density of 2.98 gm./cc., and 0.5% oxygen content, was formed into a slurry consisting of:

Parts by wt. Copper powder 120 Vistanex L-300 polyisobutylene resin 1 Naphtha 23 The slurry was spread onto a moving belt serially, in several different, separate layers, each having a thickness in the range from 0.010" to 0.070. A layer having a thickness in the lower end of this range, that is, 0.010" to 0.020, was dried at feet per minute in a vaporization furnace that was about feet long, and that was at a temperature of about 750 F. A thicker plastic strip, having a uniform thickness in the range from 0.060" to 0.070", required a lower speed, about 4 feet per minute at a furnace temperature of about 900 F. The average density of these dried plastic strips was about 3.0 gm./cc., that is, 36.5% dense as compared to the theoretical density of 8.21 gm./ cc. for the above mixture, dry basis.

Example II Copper powder having an average particle size of 0.7 micron, an apparent density of 0.63 gm./ cc. and an oxygen content of 1.38%, was formed into a slurry consist- Example III The copper powder similar to that of Example H was 7 given a heat treatment by roasting it, to increase the average particle size to 13.5 microns, and to increase the apparent density to 3.3 gm./cc. The roasting also had the advantage of insuring the removal of extraneous carbona. ceous material that may have been initially present in the copper powder as received. The roasted powder was formed into a slurry consisting of:

. Parts by wt. Copper powder 130 Vistanex L-300 polyisobutylene' resin 1 Naphtha 18.5

Slurries consisting of the components of each of the above detailed Examples I and III were spread on the stainless steel belt at a thickness of 0.07 inch. The solvent was then evaporated, and the layers were stripped from the belt and were then sintered in an atmosphere of 6% hydrogen and 94% nitrogen at 2080 F. at a speed of 6 feet per minute, in a sintering furnace 3 feet long. The sintered copper strips were coherent and had less than theoretical density. They were useful as permeable copper sheets, and could be hot or cold rolled to produce sheets of greater densities. The permeable sheets, for example, couldbe filled or coated with a resin, for use as a roofing material.

Several specimens of the slurry of Example I were cast into sheets, and after evaporation of the solvent, the coherent dry sheets were stripped from the stainless steel belt, prerolled, and then sintered, to give the results of the following Table -I:

TABLE I History Percent Theoretical Density Percent Theoretical Density Density, gin/cc.

As spread 0.069" Prerolled approx. 40% Prerolled approx. 50 Prerolled approx. 57 Prerolled approx. 66 Prerolled approx. 71% As spread 0.012 Rolled 58% after sinter As spread 0.030 Prerolled approx. Rolled 30% after sinter Prerolled 70% and Cold rolled 29% after sinter Other examples The following are examples of other metal powders and compositions or mixtures which may be used in the process of the invention:

Nickel powder:

Particle size ,u. 6.0

Apparent density gm./cc 2.64 Mixture proportion, parts by wt.:

Vistanex L-300 polyisobutylene 1 Nickel powder 100 Naphtha 18.5 Brass powder 70-30 prealloy:

Particle size ,u 14.6

Apparent density gm./cc 2.92 Mixture proportion, parts by wt.:

Vistanex L-300 polyisobutylene 1 Brass 100 Naphtha 19.9 Brass 7030 Cu-Zn powder mixture:

Particle size 7 Apparent density gm./cc 3.12 Mixture proportion, parts by wt.:

Vistanex L-300 polyisobutylene 1 Cu-Zn powder 122 Naphtha 17.7 Iron powder:

Particle size up 14.2

Apparent density gm./cc 2.54 Mixture proportion, parts by wt.:

Vistanex L-300 polyisobutylene 1 Iron 120 Naphtha 15.7 Tungsten powder:

Particle size -p. 0.9

Apparent density gm./cc 3.24 Mixture proportion, parts by wt.:

Vistanex L-300 polyisobutylene 1 Tungsten 107.5

Naphtha 17.3

The technique of using a solution of the plastic binder in a volatilizable solvent, to suspend the metal powder, has the advantage of providing a sufiiciently stable suspension that powder settling is not a problem during the application of the slurry mixture to the polished metal belt. This contributes to dimensional uniformity of the dried, coherent strip. Moreover, the fact that the dried, co herent strip is handable, and can be removed from the polished belt, permits the slurry to be applied to a belt whose temperature cycle is low, thus avoiding distortion and preserving the finish of the belt; and also permits the performance of the sintering operation on another belt, whose configuration, within reasonable tolerance limits, will not affect the dimensions or the uniformity of the coherent strip.

The process of tage of permitting having high metal-to-plastic ratios and solvents as naphtha or white gasoline, which greatly reduce the cost and the drying and sintering times. For example, by a judicious selection of copper powder size, and with the use of a minimum amount of plastic, it is possible to preroll the dry sheet up to about 75% reduction in thickness, and to produce a sintered sheet having about 82% of the theoretical density of wrought copper. When the dried, coherent sheet is prerolled to about 75% reduction, the sheet is sufficiently tough and strong that it can be pulled through the sintering furnace. When processing prerolled sheets, the sintering time may be further reduced by the elimination of a carrier belt in the sintering furnace.

the invention has the important advanthe processing of metal powder s1urr1es such inexpensive Example IV The amount of plastic binder that is used should be as low as practicable, for the reasons that have been pointed out. Preferably, just enough binder is employed to form a dried, coherent sheet that will sustain its own weight over a length of at least 15 feet. This is sufficient to permit stripping and transferring of the dried, coherent sheet. However, a greater or smaller amount of plastic may be used if the design of the apparatus imposes greater or smaller demands upon the dried, coherent sheet.

The terms sheet and strip are used interchangeably herein, to designate the essentially two-dimensional products of the invention. The invention has great anticipated application for the continuous production of a sintered copper strip having a thickness of 20 mils or less, that may be reduced by hot or cold rolling, or both, to 10 mils or less. One preferred way in which to apply the invention is for the continuous production of a sintered, hot rolled copper strip having a thickness of 6-8 mils, that is then cold rolled to 3-5 mils, to approach theoretical density.

While the invention has been disclosed by reference herein to the details of preferred embodiments thereof, it is to be understood that such disclosure is intended in an illustrative rather than in a limiting sense, and it is contemplated that various modifications will readily occur to those skilled in the art, within the spirit of the invention and the scope of the appended claims.

I claim:

1. The continuous process of making a metal sheet which comprises:

forming a slurry mixture of metal powder and a liquid formed of a heat fugitive plastic binder dissolved in a volatilizable solvent wherein the amount of said binder is up to approximately 2.5% of the weight of said metal powder,

forming a uniform layer of the mixture on a flat,

smooth supporting structure,

heating the layer to evaporate the solvent and form a tough layer of the plastic and metal powder,

removing the tough layer of metal and plastic from the supporting structure, and

passing it into a sintering operation at a temperature near the melting point of the metal under non-oxidizing conditions to remove the plastic and sinter the metal particles into a coherent sheet consisting entirely of the metal, and

passing the metal sheet between rolls to reduce its thickness and form a dense metal sheet.

2. In the process of claim 1, forming a slurry of the metal powder in a polyisobutylene having an average molecular weight of from 200,000 to 300,000 dissolved in a hydrocarbon of the group consisting of white gasoline and naphtha.

3. In the process of claim 1, forming a mixture in which the metal is copper.

4. The continuous process of making a metal sheet which comprises:

applying to a moving smooth surface of metal a continuous uniform layer of a mixture of metal powder in a liquid binder consisting of a heat fugitive resin in solution in a volatile hydrocarbon, wherein the amount of said binder is up to approximately 2.5

of the weight of said metal powder,

heating the layer of mixture to evaporate the hydrocarbon and form a dry sheet consisting of the metal powder and resin,

removing the dry sheet from the smooth surface,

prerolling the dry sheet to increase the density, and

heating the prerolled sheet of metal to remove the resin and sinter the particles while in a non-oxidizing atmosphere.

5. In the process of claim 4,

superimposing two of said dry sheets,

prerolling the two dry sheets together to form a single sheet,

heating the resulting single sheet to a sintering temperature, and then rolling the sintered sheet to form a dense sheet.

6. A continuous process of making a metal product in 7. A continuous process of making a copper strip prod- 10 a homogeneous mixture of a metal powder of the group consisting of: copper; brass alloy; a mixture of copper and zinc; a mixture of copper and nickel; iron; nickel; and tungsten, in a liquid plastic binder strip form comprising: consisting of a heat fugitive resin in solution in a forming a substantially homogeneous slurry mixture of volatile solvent wherein the amount of said binder a metal powder and a solution of a he at fugitive plasis up to approximately 2.5% of the weight of said tic binder in a volatilizable solvent wherein the metal powder; amount of said binder is up to approximately 2.5% heating the mixture to evaporate the solvent and form of the weight of said metal powder, to permit the a dry, coherent sheet consisting of the metal powder conversion of the mixture to a coherent, self-sustainand resin, said dry sheet being tough and self-suping body upon heat removal of the solvent; porting; applying said mixture to the surface of a smooth, highly removing the dry sheet from the belt;

polished, endless belt, as a homogeneous layer that heating the dry sheet to remove the resin from the has an upper surface that is disposed substantially in metal powder; and parallelism with its lower surface and with the highly further heating the sheet to its sintering temperature polished belt surface that confronts its lower surface, to sinter the particles of metal into a coherent sinand that has a transverse cross-section of substantered sheet. tially uniform thickness; 9. The continuous process of making a clad metal artitransporting said layer on said belt through a cohering le which comprises:

zone; applying to a surface of a continuously moving solid heating said layer in said cohering zone to drive off base of metal a uniform layer of a homogeneous the solvent and form a coherent strip that has submixture of a metal powder dispersed in a plastic stantially parallel major faces and a substantially binder consisting of a heat fugitive resin dissolved in niform r nsv rs r -se i a volatile solvent wherein the amount of said binder removing the strip from said belt; is up to approximately 2.5% of the Weight of said transporting said strip on a removable support through metal powder,

a heat treating zone under non-oxidizing conditions; h ti th bl f th moving Sheet d h subjecting said strip in said heat treating zone to eleplied layer of metal powder and plastic binder to vated temperatures first to drive off the plastic binder remove the solvent, and then to sinter the metal particles to fo a heating the assembly to a sintering temperature for the herent sintered metal strip that is free from the plasm tal powder, unde non-oxidizing conditions, to retiC ind r, and th n move the plastic, to sinter the particles of metal, and removing the sintefd metal Strip from Said heat treatto bond the sintered metal particles to the base, and iIlg Z0116 and from said pp subjecting the resulting product to a rolling operation to form a clad article.

10. In the process of claim 9, applying to the surface of the moving base a mixture of copper powder dispersed in a solution of polyisobutylene having an average molecular Weight of 200,000 to 300,000 in a volatilizable hydrocarbon solvent.

11. The continuous process of making a metal sheet which comprises:

uct comprising:

forming a substantially homogeneous slurry mixture of copper powder particles having a particle size predominantly in the range from about 5 microns to 4 about 44 microns and a solution of a heat fugitive plastic binder in a volatilizable solvent, wherein the amount of said binder is up to approximately 2.5%

of the weight of said metal powder to form, upon removal of the solvent and cohering of the binder, a

applying to a moving smooth surface of metal a con- 45 tinuous uniform layer of a homogeneous mixture of Coherent and Self-Sustaining y; metal powder in a liquid binder consisting of a heat pp y Said mixture to the Surface a Smooth, g y fugitive resin in solution in a volatile hydrocarbon Polished 611131685 belt, to form thereon homoghhewherein the amount of said binder is up to approxious layer that conforms to the highly polished, smooth mately 25% of the weight f d metal d belt surface and that has a transverse cross-section heating h layer f mixture to evaporate h h d of substantially uniform thickness; carbon and form a dry sheet consisting of the metal transporting said layer on said belt through a cohering Powder d i Z0116; removing the dry sheet from the smooth surface; heating Said layer in Said cohering Z0116 to drive off the superimposing the dried sheet over the clean surface solvent and to form a coherent strip that has its face of a wrought metal h that engages against the Smooth belt Surface subjecting the superimposed sheets to a prerolling optormihg t0 the finish and Shape of the belt Surface, eration to increase the density of the dried sheet; and that has a substantially uniform transverse crossheating the dried sheet to a fli i temperature t Section; remove the resin and to sinter the particles of metal, removing the coherent strip from the first belt and 0 and transferring it to a second endless belt; rolling the i d h t, transporting said coherent strip on said second belt A process f r making a clad metal strip comPristhrough a heat treating zone under non-oxidizing Conditions; forming a substantially homogeneous sl-urry mixture of subjecting said coherent strip in said heat treating zone a metal powder d a ll b fli i amount of to elevated temperatures first to drive the Plastic a solution of a heat fugitive plastic binder in a volabiflder, and then tilizable solvent, to permit the conversion of the to sinter the copper particles, to form a coherent sinmixture to a coherent, lfl u tai i g b d upon tered metal strip that is free from the plastic binder, h removal f h so1vent d i h practice f and then the present process; removing the sintered copper strip from said heat treatl i id i t t th surface f a moving b ihg Z011e and from Said Second heltstrip of metal, as a homogeneous, substantially uni- 8. The continuous process of making a metal sheet f layer; which comprises: transporting said layer on said base strip through a coapplying onto a smooth surface of a moving metal belt hering zone;

heating said layer and said base strip in said cohering zone to drive off the solvent and to form a laminate of a coherent layer on the base strip;

transporting said laminate through a heat treating zone under non-oxidizing conditions, and

subjecting said laminate in said heat treating zone to elevated temperatures first to drive off the plastic binder and then to sinter the metal particles to form a coherent sintered metal cladding on the base strip that is bonded to the base strip and that is free from the plastic binder.

References Cited UNITED STATES PATENTS 2,187,086 1/1940 Koehring 75-208 X 2,190,237 2/1940 Koehring 75-208 X 2,339,208 1/1944 Van Der Pyl 75-208 X 2,350,179 5/1944 Marvin 75-208 X 2,582,744 1/1952 Brennan 75208 X 12 Waines 75-222 X Mott 75-214 Gould et al. 75208 X Brundin 75213 Raiklen 75208 X Trotter et a1. 75-208 X Goetzel et al 29l82.1 X Mouwen 75222 Kerstetter et a1. 75208 X Long et a1. 149-19 Doe et al. 149-19 Kerstetter 29-1823 Great. Britain.

CARL D. QUARFORTH, Primary Examiner. BENJAMIN R. PADGETI, Examiner.

M. J. SCOLNICK, Assistant Examiner. 

1. THE CONTINUOUS PROCESS OF MAKING A METAL SHEET WHICH COMPRISES: FORMING A SLURRY MIXTURE OF METAL POWDER AND A LIQUID FORMED OF A HEAT FUGITIVE PLASTIC BINDER DISSOLVED IN A VOLATILIZABLE SOLVENT WHEREIN THE AMOUNT OF SAID BINDER IS UP TO APPROXIMATELY 2.5% OF THE WEIGHT OF SAID METAL POWDER, FORMING A UNIFORM LAYER OF THE MIXTURE ON A FLAT, SMOOTH SUPPORTING STRUCTURE, HEATING THE LAYER TO EVAPORATE THE SOLVENT AND FORM A TOUGH LAYER OF THE PLASTIC AND METAL POWDER, REMOVING THE TOUGH LAYER OF METAL AND PLASTIC FROM THE SUPPORTING STRUCTURE, AND PASSING IT INTO A SINTERING OPERATION AT A TEMPERATURE NEAR THE MELTING POINT OF THE METAL UNDER NON-OXIDIZING CONDITIONS TO REMOVE THE PLASTIC AND SINTER THE METAL PARTICLES INTO A COHERENT SHEET CONSISTING ENTIRELY OF THE METAL, AND PASSING THE METAL SHEET BETWEEN ROLLS TO REDUCE ITS THICKNESS AND FORM A DENSE METAL SHEET. 